Filtering using impedance translator

ABSTRACT

This disclosure relates to low noise amplifiers (LNAs) and more particularly to LNAs integrated on integrated circuit (IC) chips along with radio frequency (RF) amplifiers. In one implementation, an impedance translator is coupled to an amplifier, the impedance translator to cause the amplifier to selectively amplify the one or more components of a received signal.

RELATED APPLICATION

This Application is a Continuation of co-pending patent application Ser.No. 12/419,873, which was filed on Apr. 7, 2009. The entire contents ofthe co-pending Patent Application are incorporated herein by reference.

BACKGROUND

Mobile communication devices, such as cellular telephones (hereinafter“cell phones”), have become ubiquitous in many parts of the world. Cellphones enable the user to communicate voice and other data signalsbetween themselves, others, and various devices. The communications aretypically full duplex communications in which the cell phone transmits aradio frequency (RF) signal conveying information to a base station andreceives another RF signal from the base station which conveys certainother information to the cell phone. Thus cell phones host both an RFtramsmitter and an RF receiver. Accordingly, at least a portion of atypical cell phone (and other mobile communication devices) is referredto as an RF transceiver. Typically, the strength (as measured at thecell phone) of the RF signal transmitted from the cell phone is manydozens of decibels greater than the strength of the RF signal receivedby the cell phone.

Moreover, cell phones are typically hand held and many users value cellphones which possess small form factors. Thus, it is often the case thatthe transmitter portion of the cell phone and the receiver portion ofthe cell phone share an antenna. In the alternative, separate antennasmay be used by these portions of a cell phone. Nonetheless, because ofthe small form factor of most if not all cell phones, some of thetransmitted signal is likely to leak into the receiver of the cellphone. Moreover, the use of separate antennas increases the overall sizeof the cell phone as does adding circuitry to filter, compensate for, orotherwise eliminate the affects of the transmitted leakage signal. Othermobile communication device receivers similarly suffer from theseaffects.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different instances in thedescription and the figures may indicate similar or identical items.

FIG. 1 is a block diagram of a cellular telephone transceiver.

FIG. 2 is a bock diagram of an alternative cellular telephonetransceiver.

FIG. 3A is a schematic diagram of a cellular telephone receiver.

FIG. 3B is a schematic diagram of another cellular telephone receiver.

FIG. 4 is a schematic diagram of another cellular telephone receiver.

FIG. 5 is a schematic diagram of yet another cellular telephonereceiver.

FIG. 6 is a flow chart illustrating a method of some implementations.

DETAILED DESCRIPTION

Disclosed herein are techniques for filtering, if not eliminating,leakage signals from mobile communication device receivers and moreparticularly cell phone receivers. In one disclosed implementation, aradio frequency (RF) receiver is configured to receive an overallsignal, filter a component at a transmission frequency from the overallsignal, and amplify and output a component at a reception frequency. Thetechniques described herein may be implemented in a number of ways. Oneexample environment and context is provided below with reference to theincluded figures and on going discussion.

FIG. 1 is a block diagram of a cell phone transceiver. The transceiver100 contains a receiver 102, transmitter 104, a duplexer 106, an antenna108, a transmitter amplifier 109, a receiver low noise amplifier (LNA)110, and a filter 112. The transceiver 100 can be a portion of auniversal mobile telephone system (UMTS), a global system for mobilecommunications (GMS), a code division multiple access (CDMA), a wideCDMA (W-CDMA), etc. device. Within the receiver 102, the transceiver 100contains a conventional amplifier 114 (subsequent to LNA 110), an RFmixer 116, a filter 118, an analog to digital converter (ADC) 120, adecision feedback equalizer (DFE) 122, an oscillator 124, and associatedphase shifter 125. These components 106, 110, 112, 114, 116, 118, 120,122, 124, and 125 operate together in a conventional manner to receiveRF signals, separate the base band signal (which conveys information)from other components of the overall received signal, and amplify andoutput the base band signal. More particularly, LNA 110 is situatedclose to the antenna 108 to amplify the received signal prior to theintroduction of as many noise sources as is practicable. In situationsin which it is desired to use a differential amplication system, thereceiver 102 can include a second RF mixer 128, a second filter 130, asecond ADC 132, and a second DFE 134 to amplify the desired signal in adifferential mode and in a conventional manner.

Some of the components of the receiver 102 are shown as being integratedon a single integrated circuit (IC) chip 136. FIG. 1 also shows thatsome of the components of the transmitter 104 (not shown) can beintegrated on the same IC chip 136 as are the components of the receiver102. However, these components of the transmitter 104 and the receiver102 can be integrated on different IC chips. The duplexer 106, antenna108, LNA 110, and the filter 112 are shown as being hosted externally tothe IC chip 136 by the transceiver 100. The external hosting of theduplexer 106, the antenna 108, and the filter 112 arises because oftheir relatively large physical size. Indeed, the physical size of theantenna 108 is determined in part by the desired transmission andreception frequencies (i.e., the transmission and reception wavelengths)of the transceiver 100. The physical size of the antenna 108 in partalso determines the physical size of the duplexer 106. Thus, theduplexer 106 is also hosted externally from the IC chip 136.

The filter 112 can be either a bulk acoustic wave (BAW) or surfaceacoustic wave (SAW) filter which serves to filter certain components ofthe overall received signal from that received signal before thesecomponents reach the receiver 102. At least some of these componentsoccur at the transmission frequency of the transmitter 104 althoughfiltered components can occur at other frequencies. Typically, thefilter 112 is hosted externally to the IC chip 136 also because, inpart, because BAW and SAW filters can be large in comparison to theother components of the receiver 102.

In operation, transmitter 104 generates an RF signal which iscommunicated to transmitter amplifier 109. Amplifier 109 has a gainassociated with it which amplifies the RF signal it receives from thetransmitter 104. The amplified signal passes from the amplifier 109 tothe antenna 108 for transmission. Since cell phone transceivers 100typically use one antenna for both transmission and reception, theamplified signal passes through the duplexer 106 en route to the antenna106, ideally, the duplexer 106 would completely isolate the receiver 102from leakage of the transmitted signal into the receiver 102. However,in order to increase the degree of isolation provided by the duplexer106, it is often necessary to increase the insertion losses associatedwith the duplexer 106. Thus, it is a common practice to tradeoff thedegree of isolation and the insertion losses associated with theduplexer 106. Accordingly, typical duplexers only provide about 57decibels of isolation between the antenna 106 and the receiver 102during transmissions.

Since some of the transmission signal will therefore leak into thereception path of the cell phone transceiver 100, filtering of thatunwanted (in the receiver 102) transmission signal is desired. Otherwisethe leaked transmission signal will appear as noise in the receiver 102.As a result, it is also a common practice to place the filter 112 in thereception path as early as is practicable. However, it is also desirableto place the first stage of amplification (i.e., low noise filter 110)as early in the transmission path as is practicable to reduce the amountof noise amplified as a result. Many cell phone transceiver 100 designsfind a balance by placing the low noise amplifier 110 first and thefilter 112 second in the reception path. These designs also add a secondstage of amplification (i.e., low noise amplifier 114) to further boostthe received signal once it is relatively free of noise (andparticularly the leaked transmission signal). Thus, these designsprovide some isolation at the duplexer 106 and some isolation at thefilter 112. These designs also provide two stages of amplification. Onestage amplifies the wanted signal (received by the antenna 106) and theunwanted and leaked transmission signal. The second stage amplifier 114amplifies the received signal after it has been filtered. While thisarrangement works relatively well, it is more complicated thandesirable. FIG. 2 illustrates a cell phone transceiver 200 whicheliminates some of the complexity associated with the cell phonetransceiver 100.

FIG. 2 is a block diagram of another cell phone transceiver 200 ofvarious implementations. The transceiver 200 contains a receiver 202, atransmitter 204, a duplexer 206, and an antenna 208. Transmitter 204 andantenna 208 are similar to those shown in transceiver 100 of FIG. 1.Instead of the externally mounted filter 112 and the two amplifiers 110and 114, as illustrated in FIG. 1, cell phone transceiver 200 includesonly the low noise amplifier 210 and no SAW or BAW filter (or any otherfilter) corresponding to filter 112. Furthermore, the duplexer 206 caneven provide less isolation from the transmission signal for thereceiver 202 than the duplexer 106 (see FIG. 1). Accordingly, theduplexer 206 can have less isolation losses associated with it then theduplexer 106. For a given receiver 204, therefore, the transmittedsignal will be stronger than heretofore possible. In contrast to thecell phone transceiver 100, the cell phone transceiver 200 includes thelow noise amplifier 210 which can provide all of the desiredamplification of the received signal and which also provides isolationfrom the leaked transmission signal (and other noise). Thus, thereceiver 204 of FIG. 2 features integrated selectivity.

Thus, in operation, antenna 208 receives an overall signal which mightcontain components that are transmitted by the transmitter 204 (i.e.,the leakage signal) and possibly other noise. The duplexer 206 partiallyisolates the transmitter 204 and the receiver 202 from each other byfiltering the leakage signal from the received signal. Thus, theduplexer 206 allows two-way communications via antenna 208. However,practicable duplexers 206 cannot entirely eliminate leakage of thetransmitted signal into the receiver 202. Such signals within thereceiver 202 are often referred to as “leakage signals.”

With respect to the receiver 202, waveguides, cables, etc. within thetransceiver 200 direct the received signal (including leakage componentsat the transmission frequency) from the duplexer 206 to the receiver202. Within the receiver 202, the overall received signal is input tothe LNA 210 which 1) provides isolation from the leakage signal and 2)selectively amplifies the components of the received signal which are atthe reception frequency of the receiver 202. LNA 210 rejects componentsof the overall received signal which are at other frequencies (and, moreparticularly, those components which are at the transmission frequency).Thus, LNA 210 is centered on the reception frequency and, and selectssignals at that frequency. LNA 210 also outputs the amplified componentsto the input of the mixers 216 and 228. The mixers 216 and 228 mix theamplified components (which are at the reception frequency) and recoverthe base band signal which was originally contained within the componentof the overall received signal which is at the reception frequency.Components 218, 220, 222, 230, 232, and 234 of the receiver 204, whichare subsequent to the mixers 216 and 228, further process the amplifiedcomponents for ultimate presentation to a user (typically as audiblesignals) or to other components within the transceiver 200 (typically asdigital signals).

With continuing reference to FIG. 2, the LNA 210 can be used in avariety of applications. For instance, the LNA 210 can be incorporatedin a cell phone or other mobile communication device, coupled to theantenna thereof (either directly or indirectly by a duplexer or othercomponent), and used to selectively amplified components of the receivedsignal. More particularly, FIGS. 3-5 illustrate some implementations ofLNAs similar to LNA 210 in various cell receivers.

FIG. 3A shows a schematic diagram of a cell phone receiver of variousimplementations. The receiver 302 includes an LNA 310, a mixer 340, andan impedance translator 342. The mixer 340 accomplishes functionssimilar to components 216, 218, 220, 222, 224, 225, 228, 230, 232, and234 of FIG. 2. With continuing reference to FIG. 3, LNA 310 includesamplifier 346 and a resonant circuit such as an LC tank 348. Theamplifier 346 is configured to operate in the RF domain. The RFamplifier 346 and the LC tank 348 are wired in series between a powersupply and ground. Furthermore, the LC tank 348 is configured to centerthe RF amplifier 346 on the reception frequency of the receiver 302. Asshown, the RF amplifier 346 can be a degenerative cascode amplifier(containing metal-oxide semiconductor field-effect transistors) or itcan be some other suitable type of amplifier such as a BJT (bipolarjunction transistor) based amplifier. The mixer 340 can be connectedacross the output of the RF amplifier 346 to accept amplified componentsof the overall received signal and to further process the same.

With regard to the impedance translator 342 illustrated by FIG. 3A, itis connected in parallel with the LC tank 348 and serves to cause thereceiver 302 to selectively amplify components of the overall receivedsignal (which are at the reception frequency), to reject other signalcomponents (notably, although not limited to, components at thetransmission frequency fTx), or to perform both functions. Moreparticularly, the impedance translator 342 contains a mixer 350 and areactive component 352. As further indicated by FIG. 3A, the reactivecomponent 352 can be either a capacitor or an inductor. The mixer 350 isconnected to an alternating signal source and serves to translate thereactance to an impedance based on the frequency of the alternatingsignal.

The mixer 350 operates at either the transmission or receptionfrequency).as further disclosed herein. In some implementations whichemploy a polar modulation architecture for the cell phone's transmitter,the signal from the transmitter's local oscillator drives the mixer 350.Moreover, the transmittter's local oscillator signal can be phasemodulated to account for differing delays associated with the mixer 350and the low noise amplifier 310. Thus, the phase shifting can serve tokeep the mixer 350 and the low noise amplifier 310 in phase with eachother. In some embodiments, the mixer 350 is either a single mixer or aquadrature mixer.

When desired, the impedance translator 342 can be configured as a bandpass filter. In such implementations, the reactive component 325 is acapacitor. More specifically, the reactive component 352 is a capacitorwith a capacitance (i.e., reactance) selected so that the reactivecomponent 352 and the mixer 350 (driven by a signal alternating at thereception frequency fRx) function as a band pass filter at the receptionfrequency fRx. Accordingly, any component at the reception frequency fRxof the overall signal received by the antenna (and subsequently input tothe RF amplifier section of the LNA 310), is shorted by (i.e. passedthrough without attenuation) the reactive component 352 (here acapacitor) while unwanted signals are attenuated therein. As a result,the reactive component 352 and the mixer 350 center the LNA 310 on thereception frequency and cause it to reject signal components at thetransmission frequency fTx (among other frequencies).

In the alternative, the impedance translator 342 can be configured as anotch filter. In such implementations, the reactive component 352 is aninductor. More specifically, the reactive component is an inductor withan inductance (i.e. reactance) selected so that the reactive component352 and mixer 350 (driven by a signal alternating at the transmissionfrequency fTx) function as a notch filter centered on the transmissionfrequency fTx. Accordingly, the reactive component 352 and the mixer 350cause the LNA 310 to pass the wanted signal component (at the receptionfrequency fRx) to the mixer 240 for subsequent processing. For similarreasons, the reactive component 352 and the mixer 350 attenuate theunwanted signal component at other frequencies (such as the leakagesignal component). As a result, the LNA 310 of FIG. 3A selectivelycauses components at the reception frequency of the overall receivedsignal to be shunted through the mixer 340, further amplified, andoutput accordingly.

In some implementations, the impedance translator 342 can contain aswitch 355 connected between the mixer 350 and the LNA 310. The switch355 can be controlled by a processor (or other component) of the cellphone so that when the transmitter (not shown) is inactive, the switch355 is open. Thus, the switch 355 can prevent the impedance translator342 from consuming power during periods when the transmitter isinactive. In some implementations, the switch 355 can be opened toisolate the impedance translator 342 when the component(s) at thetransmission frequency fTx (and other frequencies other than thereception frequency fRx) of the overall received signal is below someselected value or threshold.

FIG. 3B is a schematic diagram of another cellular telephone receiver.In some implementations illustrated by FIG. 3B, the reactive componentcan be an inductor 382 fabricated using an active component configuredto give rise to an impedance Zt. More particularly, the active inductor382 can include an operational amplifier 384 with a gain of A and a pairof resistors 386 with resistance R interconnected as shown. Thisarrangement of the active inductor 382 and the mixer 350 gives rise tothe impedance Zt with increasing offset frequency from 0 Hz. Nominally,with DC (direct current) signals, the impedance Zt is equal to R/A.Thus, when the gain is very high the impedance Zt is approximately 0 forDC signals. However, with increasing frequency, the gain A of theoperational amplifier 384 decreases and therefore Zt rises. Accordingly,with AC signals of increasing frequency the impedance Zt increases.Accordingly, the operational amplifier 384 and resistors 386 emulate thebehavior of an inductor. More particularly, at about 80 MHz theimpedance Zt is approximately equal to the resistance R of the resistors386. Thus, the active inductor 382 of such implementations can beactively controlled (by varying the frequency of the driving signalbetween, for example, the transmission and reception frequencies) tocreate an impedance Zt as desired. Moreover, the active inductor 382 canbe integrated on the same IC chip as the other components of thereceiver 302.

FIG. 4 illustrates another implementation of a cell phone receiver. Thereceiver 402 includes an LNA 410, a mixer 440, and two impedancetranslators 462 and 472. Impedance translators 462 and 472 areconfigured as, respectively, notch and band pass filters. Thus,impedance translator 462 contains an inductor 466 while impedancetranslator 472 contains a capacitor 476. Moreover, impedance translators462 and 472 include mixers 464 and 474 which are driven by signalsalternating at the transmission frequency fTx and the receptionfrequency fRx, respectively. Thus, inductor 466 and impedance translator462 function as a notch filter centered on the transmission frequencyfTx and absorb components of the overall received signal at thetransmission frequency fTx. Furthermore, capacitor 476 and impedancetranslator 472 function as a band pass filter centered on the receptionfrequency fRx and shunting components of the overall received signal atthe reception frequency fRx to subsequent stages for further processing.Accordingly, the inductor 466, capacitor 476, impedance translators 462and 472, together in this implementation, center the LNA 410 on thereception frequency fRx and thereby cause the LNA 410 to selectivelyamplify signals at the reception frequency fRx while rejecting signalsat the transmission frequency fTx. Of course, in some implementations,either the combination of the inductor 466 and the impedance translator462 or the combination of the capacitor 476 and the impedance translator472 can center the LNA 410 on the reception frequency fRx.

In some implementations, the LNA 410 can be fabricated without an LCtank or resonant circuit. Indeed, in some implementations, the LC tankis replaced with a resistive load 448. Since the resistive load 448 isresistive (i.e., contains no reactive components such as inductors orcapacitors), the resistive load 448 can be fabricated on the same ICchip as the cascode amplifier 446 (or other type of amplifier) which theLNA 410 contains. As a result, these reactive components can befabricated on the IC chip on which the remainder of the receiver 402 areintegrated.

FIG. 5 is a schematic diagram of yet another cell phone receiver 502.More specifically, FIG. 5 illustrates a transistor-level implementationof a cell phone receiver 502. The receiver 502 is fabricated on an ICchip and contains a reactive component 552, a mixer 564, an LNA 510, apost-amplifier 541, and an RF mixer 543. The reactive component 552 hasan impedance of Zt and can be capacitive or inductive. Moreover, thereactive component 552 (as translated to the RF domain by the mixer)centers the LNA 510 on the reception frequency fRx and causes the LNA510 to reject received signal components at the transmission frequencyfTx or both.

The mixer 564 translates the impedance Zt of the reactive component 552to the RF domain. The mixer 564 also connects the reactive component 552in parallel across the LC tank 548 (or the resistive load in someimplementations) of the LNA 510. Moreover, the mixer 564 can containtransistors 580 which, in the implementation of FIG. 5, are similar tothe p-type or n-type MOSFETs (metal-oxide semiconductor field-effecttransistors) of the LNA 510, the post-amplifier 541, and the RF mixer543. As illustrated, the mixer 564 accepts, and is driven by, a signalalternating at either the transmission frequency fTx or the receptionfrequency fRx depending on whether it is desired for the reactivecomponent 552 and the mixer 564 to function as either a band pass filteror notch filter as disclosed herein.

With continuing reference to FIG. 5, the LNA 510 includes a cascodeamplifier 546 and an LC tank 548. However, the LNA 510 could includeother types of subcomponents such as a BJT based amplifier and aresistive load instead of the cascode amplifier 546 and the LC tank 548.Regardless of the types of subcomponents therein, the LNA 510 receivesthe overall RF signal (containing in some instances components at thetransmission frequency fTx and components at the reception frequencyfRx) and selectively amplifies the components thereof at the receptionfrequency fRx. As described herein, the reactive component 552 and themixer 564 center the LNA 510 on the reception frequency fRx and causethe LNA 510 to reject signals at the transmission frequency fTx. Thus,the LNA 510 outputs the amplified components (at the reception frequencyfRx) at its output for subsequent processing by the post-amplifier 541and the RF mixer 543.

In the implementation illustrated by FIG. 5, the receiver 502 alsocontains the post-amplifier 541 as mentioned previously. Thepost-amplifier 541 includes another cascode amplifier 581 and a currentsource 585 connected in series between a power supply and ground. Fromits input, the post-amplifier 541 accepts the amplified components ofthe overall received signal and further amplifies them by a gain of Gmas illustrated. The post-amplifier 541 outputs the resulting amplifiedcomponents to the RF mixer 543.

With regard to the RF mixer 543, it receives the amplified components(at the reception frequency fRx) from the post-amplifier 541 and mixesthat signal with a signal alternating at the reception frequency fRx. Asa result, the RF mixer 543 outputs a signal at the base band frequency(and a signal at the reception frequency fRx (caused by the interactionof the amplified components from the post-amplifier 541 and the drivingsignal of the RF mixer 543). Subsequently, additional filters (notshown) recover the baseband signal and forward it for presentation tothe user typically as an audible signal(s) or to other components of thecell phone typically as a digital signal(s).

In some implementations, the transistors 580, 582, 584, and 586 of themixer 564, the LNA 510, the post-amplifier 541, and the RF mixer543(respectively) can be the same type of transistors. For instance, thetransistors 580, 582, 584, and 586 can all be p-type or n-type MOSFETs(as shown in FIG. 5) or some other type of transistors such as BJTs.Thus, all of the components 552, 564, 510, 541, 543, and thesubcomponents thereof can be simultaneously fabricated on a single IC.However, the transistors 580, 582, 584, and 586 could be fabricated asdifferent types of transistors.

FIG. 6 is a flowchart illustrating a method of some implementations.More specifically, FIG. 6 illustrates the method 600 of receiving an RFsignal using a receiver of a mobile communication device. The method 600involves various steps such as step 602 at which an overall RF signalincluding components at the reception frequency fRx and transmissionfrequency fTx is received. At step 604, a reactance is translated to animpedance by a mixer. The translated reactance centers an LNA of thereceiver at step 606. In some implementations, an impedance can beactively controlled to create the reactance as illustrated at step 608.The components of the overall RF signal which are at the receptionfrequency fRx are selectively amplified at step 610 while the componentsat the transmission frequency fTx are rejected at step 612. At step 614,the amplified components which are at the reception frequency fRx areoutput.

Implementations disclosed herein and variations thereof provide numerousadvantages over mobile communication device receivers and, moreparticularly, conventional cell phone receivers. For instance,implementations provide LNAs with reactive components integrated on anIC chip along with the LNAs and along with the other components of thereceivers. The integrated reactive components can center the LNAs on thereception frequency and can cause the LNA to reject signals at otherfrequencies (e.g., the transmission frequency of the cell phone).Moreover, some implementations allow the LNA to be fabricated with aresistive load (instead of an LC tank) and on a single IC chip alongwith other receiver components. Furthermore, implementations allow thereceiver to be fabricated from transistors of one type (e.g., MOSFETs,BJTs, etc.) on a single IC Chip.

In operation, receivers of various implementations provide furtheradvantages. For instance, receivers of various implementations exhibitreduced, if not eliminated, transmission leakage through the LNA toother stages of the receiver. Receivers of some implementations exhibitimproved selectivity and improved noise rejection characteristics,particularly those related to noise at the transmission frequency. Thesereceivers can also be implemented in one IC chip with resulting spaceand fabrication savings for the overall unit (e.g., cell phone) intowhich they are assembled. Receivers of various implementations featureintegrated selectivity.

Specifics of exemplary methods are described herein. However, it shouldbe understood that certain acts need not be performed in the orderdescribed, and may be modified, and/or may be omitted entirely,depending on the circumstances. Moreover, the acts described may beimplemented by a computer, processor or other computing device based oninstructions stored on one or more computer-readable media. Thecomputer-readable media can be any available media that can be accessedby a computing device to implement the instructions stored thereon.

Conclusion

Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described. Rather,the specific features and acts are disclosed as preferred forms ofimplementing the claims. For example, the systems described could beconfigured as low noise amplifiers, receivers, transceivers, etc. ofvarious types of mobile communication devices other than cell phones.

The invention claimed is:
 1. A device including: a receiver having a lownoise amplifier (LNA), the LNA comprising: an amplifier configured tooperate in an RF domain, to receive a signal containing a component at areception frequency and a component at a transmission frequency, toamplify the component at the reception frequency, and to output theamplified component at the reception frequency; a first mixer; areactive device connected to the first mixer, the reactive device havinga reactance to allow the component at the reception frequency to pass; asecond mixer connected to the output of the amplifier and beingconfigured to mix the amplified component and to output a resultingsignal at a base band frequency; and a switch configured to isolate thefirst mixer from the RF amplifier when a magnitude of the component atthe transmission frequency is below a selected value.
 2. The device asrecited in claim 1, further comprising a transmitter connected to theantenna and being configured to transmit the component at thetransmission frequency via the antenna.
 3. The device as recited inclaim 2, further comprising a duplexer connected to the antenna, thetransmitter, and the RF amplifier, the duplexer being further configuredto switch the antenna between being coupled to the transmitter or the RFamplifier.
 4. The device as recited in claim 3, wherein the component atthe transmission frequency is a leakage signal.
 5. The device as recitedin claim 3, wherein the receiver is a portion of one of a universalmobile telephone system (UMTS) device, a global system for mobilecommunications (GMS) device, a code division multiple access (CDMA)device, or a wide CDMA (W-CDMA) device.
 6. The device as recited inclaim 1, wherein the reactance is to block the component at atransmission frequency.
 7. The device as recited in claim 1, wherein thecomponent at the reception frequency is unattenuated by the reactance.8. A device, comprising: an amplifier to receive a signal and to amplifyat least one or more components of the received signal; an impedancetranslator coupled to the amplifier, the impedance translator to enablethe amplifier to selectively amplify the one or more components of thereceived signal, the impedance translator having controlledfunctionality in accordance with an alternating signal received thereby;a switch coupled to the impedance translator, the switch to isolate theimpedance translator based on the one or more components of the receivedsignal; and an output stage coupled to the amplifier, the output stageto receive the selectively amplified one or more components of thereceived signal.
 9. The device according to claim 8, wherein theimpedance translator includes a reactance to enable the amplifier toselectively amplify the one or more components of the received signal.10. The device according to claim 9, wherein the reactance is acapacitance or an inductance.
 11. The device according to claim 8,wherein the impedance translator enables the amplifier to selectivelyamplify the one or more components of the received signal that is at aparticular frequency of the received signal.
 12. The device according toclaim 11, wherein the particular frequency of the received signal is areception frequency.
 13. The device according to claim 8, wherein theimpedance translator enables the amplifier to selectively reject the oneor more components of the received signal that is at a particularfrequency of the received signal.
 14. The device according to claim 13,wherein the particular frequency of the received signal is atransmission frequency.
 15. The device according to claim 8, wherein theswitch is to isolate the impedance translator when the one or morecomponents of the received signal is at a particular frequency and theparticular frequency is less than frequency value.
 16. A method,comprising: amplifying at least one or more components of a signal;enabling selective amplification of the one or more components of thesignal, the enabling performed by an impedance translator controlled inaccordance with an alternating signal received thereby; and isolatingthe impedance translator based on the one or more components of thesignal.
 17. The method according to claim 16, wherein the isolating actisolates the impedance translator when the one or more components of thesignal is at a particular frequency and the particular frequency is lessthan frequency value.
 18. The method according to claim 16, wherein theenabling act enables the selective amplification of the one or morecomponents of the signal that is at a particular frequency of thesignal.
 19. The method according to claim 16, further comprisingenabling selective rejection of the one or more components of thereceived signal that is at a particular frequency of the signal.
 20. Themethod according to claim 16, wherein the impedance translator is acapacitance or an inductance.
 21. The device according to claim 8,wherein the alternating signal is a signal alternating at a transmissionfrequency or a signal alternating a transmission frequency.
 22. Thedevice according to claim 8, wherein the switch is coupled between theimpedance translator and the amplifier.
 23. The device according toclaim 8, wherein the signal received by the amplifier includes acomponent at a reception frequency and a component at a transmissionfrequency, the switch configured to isolate the impedance translatorfrom the amplifier when a magnitude of the component at the transmissionfrequency is below a selected value.
 24. The method according to claim16, wherein the signal received by the amplifier includes a component ata reception frequency and a component at a transmission frequency, theact of isolating to isolate the impedance translator when a magnitude ofthe component at the transmission frequency is below a selected value.